The present invention relates to microfiber-based web structures suitable for absorbing discharged body fluids. Such structures can be incorporated into disposable absorbent articles such as sanitary napkins, infant diapers, adult incontinence pads and the like.
Absorbent structures which comprise entangled masses of fibers, i.e., fibrous webs, are well known in the art. Such structures can imbibe liquids, such as discharged body fluids, both by an absorption mechanism wherein fluid is taken up by the fiber material itself and by a wicking mechanism wherein fluid can be acquired by, distributed through and stored in the capillary interstices between fibers.
While absorbent capacity is a significant factor in determining the suitability of absorbent structures for use in disposable absorbent articles, other factors can also be important. For disposable absorbent articles which are worn or positioned in a particular relationship to the user's body, mechanical properties of the absorbent structures utilized in such articles are likewise relevant considerations. Thus features such as flexibility; resilience, e.g. resistance to bunching; softness; and tear resistance, e.g. strength and integrity, must generally be taken into account when selecting appropriate types of absorbent structures for use in absorbent articles. Absorbent structure properties which determine the comfort of the absorbent articles incorporating such structures are especially important in products like sanitary napkins and adult incontinence pads wherein the intimate contact of the article with the wearer's body make the comfort properties of such structures especially noticeable.
One way of imparting strength, flexibility and wet integrity to fibrous web absorbent structures has involved the use of blown microfibers in combination with staple absorbent fibers to fashion absorbent products. Anderson et al, U.S. Pat. No. 4,100,324; issued July 11, 1978, for example, discloses preparation of absorbent "fabrics" fashioned from blown microfibers and wood pulp fibers. Technology has also been developed to enhance the absorbent capacity of microfiber/staple fiber webs by incorporating therein particles of fluid-absorbent polymeric materials. For example, Kolpin/Brownlee, U.S. Pat. No. 4,429,001, issued Jan. 31, 1984, discloses sorbent sheet materials which comprise webs of entangled blown microfibers, generally absorbent staple fibers and particles of solid, high-sorbency, liquid-sorbent polymer materials.
Microfiber-based absorbent web structures of the prior art can utilize a wide variety of polymeric materials to form the microfiber component thereof. Frequently, however, the microfiber materials which provide webs with the most desirable strength, integrity, flexibility and resilience characteristics are also materials which are in and of themselves relatively hydrophobic polymers such as polyolefins, polyesters or other nonwettable polymeric materials. Absorbent webs containing such relatively hydrophobic polymeric, e.g. polypropylene, microfibers thus can be relatively poor at acquiring and distributing liquids within their structure unless steps are taken to improve the fluid handling propensity of such webs.
One technique frequently employed to improve the fluid handling characteristics of microfiber-based absorbent webs is to incorporate additional fibrous or nonfibrous particulate components into such webs as fluid distribution aids. Thus, for example, Insley; U.S. Pat. No. 4,650,479; issued Mar. 17, 1987, discloses the preparation of microfiber-based absorbent sheet products employing liquid transport fibers therein. Furthermore, both Kimberly-Clark Limited; British Patent Specification No. 2,113,731A; published Aug. 10, 1983 and the co-pending application of Weisman and Daugherty having U.S. Ser. No. 091,805; filed Sept. 1, 1987, disclose incorporation of certain kinds of non-fibrous particulate material into microfiber-based absorbent web structures in order to enhance fluid acquisition by and fluid distribution throughout such structures.
Perhaps the most common technique for enhancing the fluid acquisition characteristics of microfiber-based absorbent web structures is to incorporate a hydrophilizing agent within or onto those web components which would otherwise be unacceptably hydrophobic in nature. Common hydrophilizing agents include surfactants and/or silica, and these agents are frequently added to the microfiber-based web or web components at any suitable time before, during or after web preparation. The aforementioned Kolpin/Brownlee, Insley, Kimberly-Clark Limited and Weisman/Daugherty patent references all disclose the utilization of a hydrophilizing agent to improve the fluid handling characteristics of microfiber-based absorbent webs.
When liquid transport fibers, fluid distribution particles or hydrophilizing agents are employed, the addition of any or all of these components to microfiber-based absorbent webs tends to increase both the cost and processing complexity of preparing such structures. Furthermore, when hydrophilizing agent is incorporated in or on the relatively hydrophobic components of microfiber-based webs, the hydrophilizing effect of this treatment is generally not permanent. Prolonged contact of the hydrophilized components with aqueous fluids can cause the hydrophilizing agent to be washed away from portions of the web structure and potentially reduce fluid surface tension, such that the overall fluid management characteristics of the structure may diminish over time.
Given the foregoing considerations, there is a continuing need to identify microfiber-based absorbent web structures which provide the usual desirable strength, integrity, flexibility and resilience characteristics inherent in such structures but which also provide acceptable fluid handling and fluid management characteristics. Accordingly, it is an object of the present invention to provide improved absorbent web structures containing a particular type of hydrophilic melt blown microfibers which are especially effective at acquiring and handling the aqueous liquids such as body fluids which such structures are to imbibe.
It is a further object of the present invention to provide such microfiber-based absorbent web structures which exhibit these desirable fluid handling and fluid management characteristics without using, or with reduced use of, conventional fluid distribution aids such as transport fibers, particulate additives and/or hydrophilizing agents.
It is a further object of the present invention to provide such improved fluid handling, microfiber-based absorbent structures which retain the usual benefits afforded by microfibers in absorbent webs including desirable integrity, wet strength, flexibility and resilience characteristics.
It is a further object of the present invention to provide at reasonable cost disposable absorbent articles such as sanitary napkins, diapers, training pants, incontinence products and the like which utilize such improved microfiber-based absorbent web structures to form their absorbent cores.